Liquid crystal display (LCD) devices contain liquid crystal material operatively disposed between a pair of planar substrates. The facing surfaces of the substrates are typically coated with a continuous layer of a transparent conductive material which serves as an electrode. One may create optical changes in the liquid crystal material by applying a voltage to selected portions of the facing electrodes.
The substrates upon which the transparent conductive material is disposed is typically a high quality glass material, such as Corning 7059 glass. However, glass substrates suffer from several inherent limitations. For example, glass is relatively heavy and fragile. Accordingly, glass places significant constraints upon the manufacturing processes. Glass substrates require careful handling as they are breakable. Moreover, since glass is relatively heavy, automated fabrication machines must be built in order to accommodate the relatively heavy weight of the glass substrates.
Recent activity has aimed at fabricating LCDs with plastic substrates. Plastic substrates are attractive as they are thinner, lighter, and less susceptible to breakage than their glass counterparts. Plastic substrates also lend themselves more readily to continuous manufacturing processes. As a result, plastic substrates may ultimately lead to higher quality, lower cost displays, which are more readily adaptable to different applications.
Plastic substrates are, however, not without some problems. For example, plastic substrates are more flexible than their glass counterparts, and hence contribute to manufacturing defects. Thickness control of the plastic used in the substrate is also a problem, particularly since displays require very careful control of the spacing between the adjacent display substrates. Flexibility is further a problem in that as the display device flexes, spacing between the parallel substrates changes in localized areas, causing different responses of the liquid crystal material disposed therebetween. In order to address this problem, displays have been manufactured with edge seals and spacer beads or fibers disposed between the parallel substrates. However, the use of spacer beads or fibers contributes to other problems in manufacturing the displays. Accordingly, researchers have been working to eliminate the use of spacer beads or fibers, and have attempted to do so by using plastic display substrates with a ribbed structure. FIG. 1 illustrates an example of such a prior art ribbed structure 10. The ribbed structure 10 includes a plurality of ribs 12, 14, 16, with valleys 18, 20 disposed there between.
LCDs having ribbed substrate surfaces as illustrated in FIG. 1 have heretofore been developed for twisted nematic type LCDs. Twisted nematic displays require fiat, parallel rib and valley surfaces coated with thin alignment layers 22 (typically a polyimide), in order for the material to provide the desired optical effect. Substrate surfaces for use with these types of materials, must be substantially free from scratches or particle chips, as surface defects can degrade the image contrast of the display. Ribbed substrates such as those shown in FIG. 1 can be difficult to manufacture with defect free, fiat, square ribs and valleys. Moreover, since twisted nematic displays are polarization sensitive devices, the polymer for the substrate must be optically isotropic, or at least possess a well defined optic axis. This limits the use of many otherwise desirable polymeric materials. Moreover, full color LCDs using ribbed, polymeric substrates have not been demonstrated.
Accordingly, there exists a need for a liquid crystal display device which uses lightweight polymeric substrates, manufactured from optically anisotropic polymeric materials. There is also a need for full color LCD devices fabricated from light weight polymeric substrates.